An industrial robot is composed of interconnected robot parts such as, for example, a stand, robot arms, an arm housing, a wrist and a turn disc. Two adjoining robot parts are connected to each other so as to be rotatable in relation to each other around an axis of rotation or are linearly displaceable in relation to each other.
An embodiment of an industrial robot according to the prior art comprises a stationary foot, which is mounted to a base. The foot supports a stand that is rotatably arranged in relation to the foot about a first axis. The stand supports a first robot arm. The first robot arm is rotatable in relation to the stand about a second axis. The first robot arm supports an arm housing. The arm housing is rotatable in relation to the first robot arm about a third axis. The arm housing supports a second robot arm. The second robot arm is rotatable in relation to the arm housing about a fourth axis, which coincides with the longitudinal axis of the second robot arm. The second robot arm comprises a wrist housing. The wrist housing supports a wrist. The wrist is rotatable in relation to the wrist housing about a fifth axis. The wrist supports a turn disc, which is rotatably arranged about a sixth axis. The turn disc comprises a toolholder. The toolholder is adapted for attachment of a tool.
The wrist housing comprises two drive units which substantially determine the dimensions of the wrist housing. The wrist housing is determined by its length and turning radius. By the length of the wrist housing is meant its extent in the longitudinal direction, parallel to the centre axis of the wrist housing. By the turning radius of the wrist housing is meant its extent perpendicular to the centre axis of the wrist housing. The space within which the robot is able to move with all physical positions is referred to as operating space.
The drive units of the wrist housing comprise electric motors. The transmission means that is present between the motor and the driven unit is designated driving rope. A driving rope thus comprises gears, chains or drive belts that transmit the motor rotation to the desired rotation around each axis of rotation. Arranging the motors for driving the rotary motions of the wrist and the turn disc inside the robot arm or in the wrist housing is a known design. The arm of an industrial robot must often pass through narrow passages and work in narrow spaces. The longer and thicker a wrist housing is, the worse will be the accessibility. It is thus desirable to limit the length and the turning radius of the wrist housing. To limit the extent of a wrist housing in space, the motor that drives the movement of the wrist is often mounted at the opposite end of the robot arm.
The motors are driven by electric current via electric cabling and are controlled via signals from signal cabling. These cablings are often disposed internally of the robot arms. The tool and the functions specific for the tool are driven and controlled via process cabling. The process cabling comprises cables for power and signals, conduits for fluids and gases, and sometimes an empty bendable protective casing, which is arranged for laying one or more conduits and cables. Process cabling transports process media, such as electricity, water and air, to the tool. Process cabling is space-demanding and stiff and is often disposed outside of the robot.
Process cabling that is disposed outside of the robot is easily subjected to impacts and extreme bending. To avoid such damage, it is desirable to dispose the process cabling inside the robot. In this way, the cables are above all protected against damage caused by squeezing. In this way, the cables are also protected from extreme twisting that may lead to rupture. At the same time, loose cables are prevented from encroaching upon the operating space. Such cables make it difficult to access and perform work in narrow spaces.
It is known that motors and gears are centrally located in the wrist housing. Motors and gears are thus located in such a way as to make it impossible to dispose the process cabling internally.
WO 97/47441 describes an industrial robot with a robot arm comprising motors. From this publication it is known to place motors in a wrist housing. The object is to achieve a tight cable entry of motor cabling to the motor that controls the wrist. However, this publication only concerns motor cabling. In addition, the motors in the wrist housing are centrally placed.
WO01/39933 describes an industrial robot with a hollow robot arm. The robot arm is rotatable around its longitudinal axis. From this publication, an internal arrangement of process cabling is known. The object is essentially to bring about a controlled cable entry to the drive pulley. However, this publication does not describe how the drive motors for the wrist and the drive pulley are placed.
EP 1128937 describes a further industrial robot with a hollow robot arm. From this publication it is known to dispose cabling internally of a robot arm. The publication also relates to a control device for controlling said cabling. The object is to protect the cabling by an internal arrangement of the cables in the robot arms. However, this publication only concerns the arrangement of cabling in the interior of a robot arm.
Thus, there is a need in industry to be able to utilize an industrial robot which has a compact wrist housing comprising drive units and which is able to work in small spaces. There is also a need in industry to be able to utilize process cabling that has a long service life and that does not encroach upon the operating space.